For nanotechnological applications, the use of thin films of materials is highly preferred. See, for example, R. A. Segalman, Materials Science and Engineering, 2005, volume R48, page 191 ff.; M. Li and C. K. Ober, Materials Today, 2006, volume 9, page 30 ff.; C. J. Hawker and T. P. Russell, MRS Bulletin, 2005, volume 30, page 952 ff.; and M. Li, C. A. Coenjarts, and C. K. Ober, Advances in Polymer Science, 2005, volume 190, page 183 ff. It would be desirable, in the case of block copolymers (BCPs), to have the nanoscopic domains, sometimes referred to as microdomains, oriented in a specific direction with a long-range lateral order for applications such as polarizers (see, for example, V. Pelletier, K. Asakawa, M. Wu, D. H. Adamson, R. A. Register, and P. M. Chaiken, Applied Physics Letters, 2006, volume 88, page 211114 ff.), templates for pattern transfer to generate microelectronic integrated circuits (see, for example, C. T. Black, IEEE Transactions on Nanotechnology, 2004, volume 3, page 412 ff.), magnetic media (see, for example, C. A. Ross, Annual Review of Materials Research, 2001, volume 31, page 203 ff.), and optical waveguides (see, for example, C. A. Ross, Annual Reviews of Materials Research, 2001, volume 31, page 203 ff.; and S. A. Maier, M. L. Brongersma, P. G. Kik, S. Meltzer, A. A. G. Requicha, and H. A. Atwater, Advanced Materials, 2001, volume 13, page 1501 ff.). In recent years, a number of approaches have been developed to control the orientation and enhance the lateral order of the microdomains by applying external fields, such as electric fields (see, for example, T. Thurn-Albrecht, J. DeRouchey, and T. P. Russell, Macromolecules, 2000, volume 33, page 3250 ff.), shear (see, for example, M. A. Villar, D. R. Rueda, F. Ania, and E. L. Thomas, Polymer, 2002, volume 43, page 5139 ff.), temperature gradients (see, for example, J. Bodycomb, Y. Funaki, K. Kimishima, and T. Hashimoto, Macromolecules, 1999, volume 32, page 2075 ff.), graphoepitaxy (see, for example, R. A. Segalman, H. Yokoyama, and E. J. Kramer, Advanced Materials, 2001, volume 13, page 1152 ff.), chemically patterned substrates (see, for example, M. P. Stoykovich, M. Müller, S. O. Kim, S. O.; Solak, H. H.; Edwards, E. W.; de Pablo, J. J.; Nealey, P. F. Science 2005, volume 308, page 1442 ff.), controlled interfacial interactions (see, for example, P. Mansky, Y. Liu, E. Huang, T. P. Russell, and C. J. Hawker, Science, 1997, volume 275, page 1458 ff.; and E. Drockenmuller, L. Y. T. Li, D. Y. Ryu, E. Harth, T. P. Russell, H. C. Kim, and C. J. Hawker, Journal of Polymer Science, Part A: Polymer Chemistry, 2005, volume 43, page 1028 ff.), zone casting (see, for example, C. Tang, A. Tracz, M. Kruk, R. Zhang, D.-M. Smilgies, K. Matyjaszewski, and T. Kowalewski, Journal of the American Chemical Society, 2005, volume 127, page 6918 ff.), optical alignment (see, for example, Y. Morikawa, S. Nagano, K. Watanabe, K. Kamata, T. Iyoda, and T. Seki, Advanced Materials, 2006, volume 18, page 883 ff.), solvent fields (see, for example, G. Kim and M. Libera, Macromolecules, 1998, volume 31, page 2569 ff.; M. Kimura, M. J. Misner, T. Xu, S. H. Kim, and T. P. Russell, Langmuir, 2003, volume 19, page 9910 ff.; S. Ludwigs, A. Böker, A. Voronov, N. Rehse, R. Magerle, and G. Krausch, G. Nature Materials, 2003, volume 2, page 744 ff.; S. H. Kim, M. J. Misner, T. Xu, M. Kimura, and T. P. Russell, Advanced Materials, 2004, volume 16, page 226 ff.; R.-M. Ho, W.-H. Tseng, H.-W. Fan, Y.-W. Chiang, C.-C. Lin, B.-T. Ko, and B.-H. Huang, Polymer, 2005, volume 46, page 9362 ff.; Z. Lin, D. H. Kim, X. Wu, L. Boosanda, D. Stone, L. LaRose, and T. P. Russell, Advanced Materials, 2002, volume 14, page 1373 ff.; J. Hahm and S. J. Sibener, Langmuir, 2000, volume 16, page 4766 ff.; and S. Park, B. Kim, J.-Y. Wang, and T. P. Russell, Advanced Materials, 2008, volume 20, page 681 ff.), and so on. Solvent evaporation is a strong and highly directional field. Making BCP thin films under various solvent evaporation conditions has been found to be a good way to manipulate the orientation and lateral ordering of BCP microdomains in thin films Kim et al. first reported that solvent evaporation could be used to induce the ordering and orientation of BCP microdomains. G. Kim and M. Libera, Macromolecules, 1998, volume 31, page 2569 ff. Vertically aligned cylindrical polystyrene microdomains could be obtained in polystyrene-b-polybutadiene-b-polystyrene triblock copolymer thin films with a thickness of about 100 nanometers. The same effect was also observed in polystyrene-b-poly(ethylene oxide) (PS-b-PEO) and polystyrene-b-poly(L-lactide) BCP thin films and was attributed to a copolymer/solvent concentration gradient along the direction normal to the film surface giving rise to an ordering front that propagated into the film during solvent evaporation. R.-M. Ho, W.-H. Tseng, H.-W. Fan, Y.-W. Chiang, C.-C. Lin, B.-T. Ko, and B.-H. Huang, Polymer, 2005, volume 46, page 9362 ff.; Z. Lin, D. H. Kim, X. Wu, L. Boosanda, D. Stone, L. LaRose, and T. P. Russell, Advanced Materials, 2002, volume 14, page 1373 ff. This orientation was independent of the substrate. However, the lateral ordering of the cylindrical microdomains was poor. Hahm et al. and later Kimura et al. showed that evaporation-induced flow in solvent cast BCP films produced arrays of nanoscopic cylinders oriented normal to the surface with a high degree of ordering. J. Hahm and S. J. Sibener, Langmuir, 2000, volume 16, page 4766 ff.; and M. Kimura, M. J. Misner, T. Xu, S. H. Kim, and T. P. Russell, Langmuir, 2003, volume 19, page 9910 ff. Recently, Ludwigs et al. demonstrated that solvent annealing could markedly enhance the ordering of BCP microdomains in thin films S. Ludwigs, A. Böker, A. Voronov, N. Rehse, R. Magerle, and G. Krausch, G. Nature Materials, 2003, volume 2, page 744 ff. By controlling the rate of solvent evaporation and solvent annealing in thin films of PS-b-PEO, Kim et al. achieved nearly-defect-free arrays of cylindrical microdomains oriented normal to the film surface that spanned the entire films S. H. Kim, M. J. Misner, T. Xu, M. Kimura, and T. P. Russell, Advanced Materials, 2004, volume 16, page 226 ff. Moreover, the use of a co-solvent enabled further control over the length scale of lateral ordering. The most recent results showed that perpendicular cylindrical microdomains oriented normal to the film surface could be obtained directly by spin-coating polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCPs from mixed solvents of toluene and tetrahydrofuran (THF) and arrays of highly ordered cylindrical microdomains formed over large areas after exposing the films in the vapor of a toluene/THF mixture. This process was independent of substrate, but strongly depended on the quality of the solvents for each block and the solvent evaporation rate. S. Park, J.-Y. Wang, B. Kim, W. Chen, and T. P. Russell, Macromolecules 2007, volume 40, page 9059 if But, the ultimate achievable data storage density achievable with these BCPs will not exceed 1 terabit per square inch (Tbit/in2). Processes to use alternate BCPs, like PS-b-P4VP or PS-b-PEO containing salt, have been developed that are simpler to employ and, more importantly, the interactions between the segments of the copolymer are very non-favorable, making defects energetically costly and, also, opening an avenue to smaller domain sizes and separation distances. S. H. Kim, M. J. Misner, L. Yang, O. Gang, B. M. Ocko, T. P. Russell, Macromolecules 2006, volume 39, page 8473 ff.
Several methods have been developed to prepare nearly perfect patterns in polymer surfaces on substrates. Conventional photolithography, electron beam (e-beam) lithography, and scanning force probe lithography are accessible techniques for fabrication of nanometer-size patterns. For example, Schmidt and co-workers showed the successful electrochemical modification of self-assembled monolayers at positions where a conductive scanning probe was in contact with a self-assembled monolayer. D. Wyrwa, N. Beyer, and G. Schmid, G. Nano Letters, 2002, volume 2, page 419 ff. The induced chemical contrast was used to guide the covalent binding of Au crystals from solution. E-beam lithography is a common method for fabrication of sub-micrometer structures. Although a beam of electrons may be focused to less than 1 nanometer in diameter, the resolution is limited by the interaction of the beam with the resist material and by the radius of gyration of the macromolecules, which is usually a few nanometers. See, for example, J. M. Gibson, Physics Today, 1997, volume 50, page 56 ff. New developments in using self-assembled monolayers overcome these restrictions inherent with standard resist materials as their thickness is usually a few angstroms. Structures as small as a few nanometers were fabricated by using this concept. See, for example, A. Gölzhäuser, W. Eck, W. Geyer, V. Stadler, T. Weimann, P. Hinze, and M. Grunze, Advanced Materials, 2001, volume 13, page 806 ff.; R. Glass, M. Arnold, E. A. Cavalcanti-Adam, J. Blümmer, C. Haferkemper, C. Dodd, and J. P. Spatz, New Journal of Physics, 2004, volume 6, page 101 ff.; and S.-M. Yang, S. G. Jang, D.-G. Choi, U.S. Pat. No. 7,081,269 B2 (2006). However, these approaches require expensive equipment and high-energy doses, and they are not suitable for non-conductive substrates unless additional treatment is carried out. Moreover, e-beam patterning is a time-consuming serial process not suitable for large areas.
It is highly desirable to develop parallel processes where the sequential generation of nanoscopic features is avoided and the patterning is achieved in one step. Nanoimprint lithography (NIL) is one such process to control the positional order of the microphase separated morphology. NIL can be used for locally controlling the self-assembly process of block copolymers and determining the precise positioning of the phase-separated domains via the topography of mold, rather than the substrate. NIL creates features by a mechanical deformation of a polymer film by pressing a hard mold into the film at temperatures higher than the glass transition temperature of the polymer. This high-throughput, low cost process is not diffraction limited, and sub-10 nanometer resolution has been reported. See, for example, S. Y. Chou, P. R. Krauss, W. Zhang, L. Guo, and L. Zhuang, Journal of Vacuum Science and Technology B, 1997, volume 15, page 2897 ff.; H.-W. Li and W. T. S. Huck, Nano Letters, 2004, volume 4, page 1633 ff.; S. Y. Chou, U.S. Pat. No. 5,772,905 (1998); and J.-H. Jeong, H. Sohn, Y.-S. Sim, Y.-J. Shin, E.-S. Lee, and K.-H. Whang, U.S. Pat. No. 6,943,117 B2 (2005). Yet, NIL has the limitation that it requires a master that is used for the printing and, as of yet, it has not been possible to generate a perfect master with uniform, nanoscopic features sizes less than 20 nanometers over large lateral distances while maintaining the features in register.